1. Field of the Invention:
The invention relates to well packers adapted to be set in packed-off condition in a well casing, or similar conduit strings, which are subsequently exposed to high temperature steam.
2. Description of the Prior Art:
Well packers have heretofore been set in well bores and subjected to high temperature steam. For example, in secondary or tertiary recovery of production from well bores, a well packer may be used in connection with the injection of high temperature steam within the surrounding formation. Temperature changes occur as a result of the varied rate at which the steam is injected through the packer into the surrounding well bore and the inherent pressure of the steam applies a significant force to the packer. Well packers under such conditions tend to loosen and leak for several reasons. These include the extrusion of the packing material through clearing spaces in the packer and between the packer and the surrounding well conduit, and also due to expansion and contraction of the packer parts due to the substanital temperature changes. Leakage is also encountered in the slick joint normally provided between the production tubing and the packer.
Packers have been specifically designed to operate under such high temperature and high pressure conditions, for example, see U.S. Pat. Nos. 3,131,764 to J. F. Muse et al and 4,307,781 to Preston, Jr. et al. These packers, as well as others existing in the prior art, have not been completely satisfactory for use in steam treatment of wells. In the first place, such packers have relied upon either asbestos or elastomeric materials to form the external and internal packing elements of the packer. Asbestos is obviously undesirable in the modern world due to its potential carcigenic effects upon people handling or fabricating the seals. Elastomeric seals are generally formed of organic materials which are subject to substantial degradation at temperatures in excess of 400.degree. F. It is therefore desirable that a packer be available that will withstand temperatures up to 700.degree. F. and steam pressures on the order of 2,500 pounds per square inch without resulting in leakage or degradation of the seal element. Also, such packer should minimize heat loss from the steam passing downwardly through the slick joint commonly provided in such packers.
This invention provides a high temperature resistant packer composed primarily of two tubular assemblies. An inner tubular body assembly is detachable securable to the bottom end of a tubing string by a left-hand threaded connection to a connector sub to effect the running in and setting of the packer. An outer operative tubular assembly is provided including, in vertically downward sequence, a drag block unit, a connecting block, a slip and cone assemblage incorporating both upper and lower cones with the upper cone abutting the connecting block, a packing assembly abutting the lower cone, an abutment element abutting the lower end of the packing element to apply an axial compressive force thereto, and a detachable connection mechanism operative between the abutment element and the lower portions of the inner tubular body assembly.
The connecting block incorporates a radially disposed J-pin which projects into a J-slot provided on the exterior of the inner tubular body assembly. During run-in, the cooperation of the J-pin with the J-slot prevents any relative axial displacement of the inner tubular body assembly with respect to the outer operative assembly. When the packet is positioned at the desired location in the well bore, generally above the formation to be steam treated, the inner tubular body is rotated approximately 90 degrees to the left to bring the J-pin into an axially elongated portion of the J-slot, thus permitting relative upward movement of the inner tubular body assembly with respect to the outer operative tubular assembly. Application of a vertically upward force to the inner tubular body assembly by the tubing string to which it is connected, applies an axial force to the packing element which in turn is transmitted to the lower cone and then transmitted through the slip to the upper cone which is held in a fixed position by the connecting block. The connecting block is further provided with a radially shiftable detent which cooperates with ratchet-like threads on the periphery of the internal body assembly to lock the body assembly against any subsequent downward displacement with respect to the outer tubular body assembly. Thus, the axial force imparted to the packing element and to the slip and cone unit are trapped therein by the cooperation of the detent in the connecting block with the ratchet threads. The upward movement of the inner tubular body assembly is discontinued when the resisting force indicates that the slips have been moved into biting engagement with the casing wall and the packing element expanded into sealing engagement with the casing wall.
Weight is then set down on the packer unit to remove any slack that might exist in the slip and cone assemblage. The packer is then pressure tested through the application of pressure to the casing annulus above the packer. If the testing indicates the packer is satisfactorily set and sealed, the tubing string is rotated to the right to disconnect the inner tubular assembly from the connector sub. Steam is introduced through the tubing string and the third element of the packer, which comprises a mandrel or slick joint threadably secured to the connector sub and having sealing engagement with an internal packing element provided in the bore of the inner tubular body assembly. Such mandrel is preferably fabricated with a double-wall insulated configuration so as to minimize the loss of the heat transfer from this internal portions of the mandrel which are exposed to steam to those external portions which are surrounded by water and well fluids.
Additionally, the internal packing element constitutes a special assemblage of non-elastic seal elements formed of materials that are not thermally degradable at temperatures up to 700.degree. F. and are assembled into an internal recess provided on the internal tubular body assembly to sealingly cooperate with the cylindrical periphery of the mandrel or slick joint. The mandrel or slick joint is preferably insulated to minimize heat loss from the downwardly flowing steam.
The aforedescribed packer obviously includes a plurality of patentable inventions. The particular invention defined by the claims of this application constitutes the construction of the outer and inner packing elements.
The primary sealing elements incorporated in both the external packing element and the internal packing element are formed primarily of graphite, and preferably a mixture of graphite and carbon oxide ash. The external packing element, which is continuously subject to the high pressure accompanying the introduction of high temperature steam into the well employs a plurality of discs of such graphite material which are disposed in an axial stack with annular pieces of wire netting located between each graphite disc and at each end of the stack of graphite discs. The entire assemblage is then die-formed so as to deform the discs into an angular or dish-shaped configuration and, at the same time, intimately incorporate the annular wire mesh elements into the structure of the graphite discs. The application of a compressive force to such die-formed assemblage will result in the assemblage tending to move back towards the original radial form of the discs, thus expanding the periphery of the die-formed assemblage into intimate sealing engagement with the bore wall of the well conduit.
In both the external and internal packing elements, the axial compression force is transmitted to the graphite elements by annular blocks of die-formed wire mesh which are originaly formed in a non-perpendicular parallelogram cross-section, but are deformed through the application of compressive forces into a substantially perpendicular parallelogram. For the external packing element, the die-formed metallic mesh rings may be fabricated from stainless steel or similar chemical-resistant material. For the inner packing element, which must accommodate relative axial movement of the mandrel with respect to the packing element, the die-formed, chemically resistant, metallic mesh is formed from a relatively soft metal such as nickel. Scratching of the mandrel surface is thereby avoided but, at the same time, extrusion of the graphite sealing elements is substantially eliminated by the essentially zero clearance provided between the metallic mesh rings and the concentric walls of the elements being sealed by the graphite members.
With the aforedescribed construction, the fluid pressure generated by the high temperature steam introduced into the production formation below the packer, is applied as a direct axial force to the external packing elements, and, through such elements, to the slip and cone assemblies to further increase the forcible contact of the packing elements with the casing bore and the biting engagement of the slips with such casing bore.
The thermal expansion and contraction of the tubular string relative to the set packer is readily absorbed by the elongated insulated mandrel or slick joint which permits movement of the tubing string in either direction relative to the set packer.
If, for any reason, it is desired to remove the packer from the well casing, such removal may be accomplished by manipulation of the tubular mandrel which is always threadably connected to the tubular string extending to the well surface. A release abutment is provided on the bottom portions of the tubular mandrel in a position below the outer operative tubular assemblage. Such release abutment is engagable with the detachable connection mechanism that is normally operatively connected between the abutment element and the lower portions of the inner tubular body assembly. Such engagement is effected by upward movement of the tubing string and, after the shearing of shear screws, effects the release of the detachable connection mechanism so that the outer operative tubular assembly is disengaged from the inner tubular body assembly. This relieves the axial force applied to the external packing elements, hence permitting that assembly, as well as the lower cone element, to shift downwardly with respect to the inner tubular body assembly. Hence, the slips may be released from their biting engagement with the casing wall and the entire packer removed by an abutting connection between the releasing abutment carried on the bottom portion of the double walled mandrel or slick joint and the bottom portions of the inner tubular body assembly, plus an abutment shoulder on the inner tubular body assembly engaging the bottom portions of the outer operative tubular assembly.
Further advantages of the invention will be readily apparent to those skilled in the art from the following detailed description, taken in conjunction with the annexed sheets of drawings, on which is shown a preferred embodiment of the invention.